The invention relates on the one hand to an apparatus for moulding plastic preforms into plastic containers, comprising a clean room, at least one blow station comprising a blow mould for shaping the plastic preforms by means of at least one process pressure, and a venting device for venting the process pressure or a process pressure reduced to a recovery pressure into the atmosphere, which venting device comprises at least one venting valve, by means of which the process pressure or the recovery pressure can be vented into the atmosphere via a sound absorber.
On the other hand, the invention relates to a method for moulding plastic preforms into plastic containers using a blow mould in a clean room, wherein the plastic preforms are moulded in the blow mould by means of a first process pressure, wherein the pre-moulded plastic preforms are subsequently finish-moulded in the blow mould by means of a second process pressure, and wherein the second process pressure is vented into the atmosphere via a venting valve immediately after finish-moulding or is reduced to a recovery pressure and the recovery pressure is vented into the atmosphere via the venting valve.
Generic apparatus and methods are well known from the prior art.
For example, international patent application WO 2010/020529 A2 describes an apparatus for moulding plastic preforms into plastic containers, which comprises a conveying device with a plurality of blow stations and a clean room. The clean room can be used to ensure good aseptic conditions during the production of the plastic preforms and also during the filling thereof with beverages. In order to be able to reduce the sterilisation efforts in this respect, the area of the conveying device on the moulding apparatus, where the blow stations are arranged, is disposed within the clean room and at least one further area of the conveying device is disposed outside of the clean room. In this way, particularly the size of the clean room can be reduced, as a result of which the areas to be sterilised on the moulding apparatus can be kept particularly small. The subject matter of WO 2010/020529 A1 is herewith included in its entirety by reference in the subject matter of the present description.
From European patent specification EP 1 271 029 B1, an apparatus comprising a blow station for blow moulding containers is known, wherein a blow pressure for blow moulding the containers is controlled by a modified device for the pneumatic control of a blow pressure, as a result of which a control pressure required for the device can advantageously be reduced.
In addition, an apparatus for blow moulding preforms in particular into bottles by means of a process pressure is known from patent specification U.S. Pat. No. 7,320,586 B2, according to which the process pressure can be at least partially recovered as a recovery pressure in a pressure vessel provided for this purpose, before a correspondingly reduced residual pressure is vented into the open environment.
As a rule, the process pressures required for moulding are wholly or partially vented into the environment via corresponding sound absorbers, in order to achieve in this way a reduction of the sound level in an advantageous manner. Such sound absorbers are often designed as multi-layered structures and as a result have a large number of gaps in which especially germs can grow. In this respect there is a risk that the germs will spread in particular starting from the sound absorber into the clean room and can contaminate the devices or preforms and/or finish-expanded containers present there. For this reason, in particular the sound absorbers are serviced or replaced with an appropriate frequency which, however, is cumbersome and moreover incurs large costs.
It is the object of the present invention to avoid this drawback.
According to a first aspect of the invention, the present object is achieved by means of an apparatus for moulding plastic preforms into plastic containers, which comprises a clean room, at least one blow station comprising a blow mould for shaping the plastic preforms by means of at least one process pressure, and a venting device for venting the process pressure or a process pressure reduced to a recovery pressure into the atmosphere, wherein the venting device comprises at least one venting valve, by means of which the process pressure or the recovery pressure can be vented into the atmosphere via a sound absorber, said apparatus being characterised by a pressure drop safety device for closing the venting valve before the atmospheric pressure level on the venting device is reached.
By means of the pressure drop safety device according to the invention it is ensured in an advantageous manner that on the venting valve, a flow direction of a pressure means for moulding the plastic preforms will always only be directed out of the venting device, as a result of which it is prevented in a constructively very simple manner that germs from outside of the clean room can get through the venting device, in particular through the venting valve, into the clean room and can contaminate said clean room.
Insofar it is advantageous if the venting valve is closed before atmospheric pressure is reached. This reduces the risk of germs getting into a plastic container or into a sterile zone of the present apparatus. Preferably, the venting valve is closed at the latest when a predefined positive pressure is reached in the finish-blown plastic container, as will be explained below. This measure ensures an air flow in just one direction and thus prevents the spreading of germs in the direction of the plastic container. Ideally, any residual pressure will be vented out of the plastic container when a corresponding blow nozzle is lifted off. This allows in an advantageous manner the use of hygienically non-optimised sound absorbers.
The object of the invention is also achieved by means of a method for moulding plastic preforms into plastic containers using a blow mould in a clean room, wherein the plastic preforms are pre-moulded in the blow mould by means of a first process pressure, wherein the pre-moulded plastic preforms are subsequently finish-moulded in the blow mould by means of a second process pressure, and wherein the second process pressure is vented into the atmosphere via a venting valve immediately after finish-moulding or is reduced to a recovery pressure and the recovery pressure is vented into the atmosphere via the venting valve, said method being characterised in that the venting valve is closed whilst the process pressure or the recovery pressure is being vented, before or as the atmospheric pressure level is reached.
Ideally, the venting valve will already be closed during a venting process before the atmospheric pressure level is reached, as a result of which any contamination can be precluded.
With regard to an alternative process, the venting valve could also be closed whilst the atmospheric pressure level is being reached, but this would cause an increased risk of germs spreading into the venting valve and in the direction of the clean room.
According to a further aspect of the invention, the present object is achieved also by means of an apparatus for moulding plastic preforms into plastic containers, which comprises a clean room, at least one blow station comprising a blow mould for shaping the plastic preforms by means of at least one process pressure, and a venting device for venting the process pressure or a process pressure reduced to a recovery pressure into the atmosphere, wherein the venting device comprises at least one venting valve, by means of which the process pressure or the recovery pressure can be vented into the atmosphere via a sound absorber, said apparatus being characterised in that the venting device includes a pressure drop safety device with means for maintaining an anti-contamination pressure at least on the venting valve, said anti-contamination pressure being between the process pressure or recovery pressure and atmospheric pressure.
Contamination of components and/or assemblies of the moulding apparatus within the clean room is prevented in a particularly simple manner by maintaining the pressure in particular in the venting device always above atmospheric pressure until the venting valve is closed.
By means of this bodiless germ barrier, any crossing over of germs from outside of the clean room into the clean room can be prevented in an extraordinarily simple manner. In particular, the bodiless germ barrier proposed herein is substantially maintenance free.
Preferably, in particular on the venting valve prior to it being closed, there will always be an anti-contamination pressure at a level between the process or recovery pressure and atmospheric pressure.
In this respect, an advantageous process variant provides for an anti-contamination pressure that is always above atmospheric pressure to be at least temporarily adjusted at a connection side of the venting valve, which faces the blow mould.
Moreover, it is advantageous for the anti-contamination pressure to be at a level of less than 5 bar, preferably at a level of less than 2 bar, so that this low pressure can advantageously be vented also by lifting off a blow nozzle directly on the blow station in a constructively simple manner. As a result, a further venting valve within the clean room may be dispensed with.
A further advantageous process variant provides for the anti-contamination pressure to be vented into the clean room and in particular on the plastic container, as a result of which a relief of the overall pressure can be achieved in a particularly simple manner from a process engineering point of view.
It goes without saying that the pressure drop safety device according to the invention and in particular also the means thereof for maintaining the anti-contamination pressure may be designed in a variety of ways.
A first embodiment, which is particularly simple in design, provides for the pressure drop safety device for closing the venting valve to comprise a mechanical pre-tension spring for a mechanically actuatable valve piston, in particular for a spring-loaded valve piston. This variant is particularly trouble-free and therefore also very low in maintenance.
The spring-loading can here be adjusted in such a way that once a predefined process pressure in the plastic container has been reached, the valve piston is displaced by spring force into a closing position.
Advantageously, the strength of such a pre-tension spring is selected or adjusted as a function of a desired closing time of the venting valve or of a desired anti-contamination pressure. A pretension of the spring can be pre-adjusted by means of a mechanism.
With regard to an alternative embodiment it is advantageous if for closing the venting valve, the pressure drop safety device comprises a pneumatic pre-tension spring for a valve piston that can be actuated in a contactless manner, in particular a pneumatically spring-loaded valve piston. As a result, a particularly low-friction pre-tension spring can be realised.
Such a pneumatic pre-tensioning constitutes an additional control piston. The air pressure can be adjusted by means of a pressure controller in such a way that once a predefined process pressure in the plastic container is reached, the valve piston closes as a result of pneumatic pretension. In order to be able, if necessary, to dispense with the additional pressure controller for pneumatic pre-tensioning, the control air that is already present on the apparatus could be used.
Here, a pneumatic pre-tensioning piston diameter may be selected such that the venting valve closes once the predefined process pressure in the plastic container is reached. In this respect, the closing force can be adapted in a constructively simple manner via the level of pressurised air and/or via the size of the piston diameter.
A further preferred embodiment provides for the pressure drop safety device for closing the venting valve to comprise a valve piston that can be actuated by means of a pneumatic control valve, which pneumatic control valve is controllable as a function of an anti-contamination pressure. As a result, an extraordinarily high level of flexibility can be achieved when adjusting the anti-contamination pressure or a closure time of the venting valve.
The pressure drop safety device may be realised in a constructively very simple manner if the pressure drop safety device comprises the venting valve. As a result, the pressure drop safety device may advantageously be at least partially integrated straight into the existing venting valve.
In order to be able to close the venting valve at the right time before atmospheric pressure is reached, it is advantageous if the pressure drop safety device comprises means for detecting a process pressure or recovery pressure on the clean room side and/or on the blow mould side.
If necessary, any pressure sensors already present on the moulding apparatus may be used for this purpose.
In addition or alternatively, a check valve may be provided on or in the area of the venting device. By means of such a check valve, any risk of an air flow directed into the clean room may also be reduced.